Museum let visitors view radioactive minerals

The Natural History Museum reassured rock lovers yesterday after pleading guilty to charges of exposing staff and the public to hot spots of radiation in its minerals gallery.

A court heard how hundreds of rocks in the ornate gallery, where specimens of rare and exotic minerals are laid out in glass cases for public display, contained far higher levels of radioactive metals than curators knew.

Even when the radioactive rocks were discovered, the museum kept the gallery open to the public for five months, removing the specimens piece by piece in a clandestine after-hours operation which would never have come to light had the health and safety executive not decided to prosecute.

One case, displaying thorite, was beaming out 50 microsieverts an hour of ionising radiation - 50 times the target figure in the museum's own radiation plan. Many natural rocks contain traces of radioactive uranium and thorium.

The museum thought it had purged the gallery of radioactive rocks after a major sweep in the 1970s. But during a change of radiation protection supervisers in the gallery in 1999, a dosimeter began to register unexpected swings.

Blackfriars crown court heard how the museum cleared the rocks between May and October 1999, in consultation with the national radiological protection board. The HSE found out in November and decided to prosecute.

The museum yesterday pleaded guilty to three charges, one of breaching the Health and Safety Act and two of breaking regulations on ionising radiation.

Pascal Bates, prosecuting, said one of the museum's executives had referred to "a collective management blindness" over the issue.

Defending, Malcolm Fortune said: "The public can be reassured that all action has been taken to remove radioactive material from the mineral galleries and, indeed, throughout the museum. Procedures are in place to avoid any repetition."

Of the 1.8m visitors to the museum each year, relatively few go to look at the minerals. Mr Fortune said consultants had worked out that even a rock enthusiast who had visited the old, radioactive specimens twice a year, spending three hours there on each occasion and spending half an hour in front of the risky rocks would receive only 44.5 microsieverts.

The recommended annual maximum radiation dose for a member of the public is 5,000 microsieverts. Eating a kilogramme of Brazil nuts or mussels, or flying from Manchester to Malaga, would give comparable doses to the old minerals gallery, Mr Fortune said.

Accepting Mr Fortune's argument that the public had not been placed at risk, the judge, John Samuels, gave the museum a conditional discharge for 12 months and ordered it to pay costs of £6,300.